Coatings and films incorporating graphene have recently come to commercial prominence due to market demand for stronger, more durable and environmentally friendly solutions.
Due to its unique properties (e.g. chemical inertness, impermeability, friction and anti-wear good properties and high conductivity), use of graphene is growing for protective and /or functionalized coatings. Applications of graphene under development in the coatings sector include:
- Electrically conducting coatings
- Heat transfer coatings
- Barrier materials
- Transparent electrode coatings
- Pressure sensitive coatings
- Sensing coatings (stimuli responsive)
- Anti-corrosion coatings.
Barrier properties
Graphene demonstrates excellent potential as a protective layer, due to its exceptional thermal and chemical stability and impermeability. The surfaces of sp2 carbon allotropes form a natural diffusion barrier, thus providing a physical separation between the protected surface and re-actants.
Graphene can be utilized as a filler for polymer matrix nanocomposite coatings, and in combination with nanoparticles to form a graphene-nanoparticles composites coating and high quality coating materials solely.
Superhydrophobicity
Graphene is a superhydrophobic and olephobic material and Graphene Oxide (GO) is hydrophilic.
Chemical and wear resistance
High anti-friction and high wear resistance properties have also been reported. Graphene is also resistant to attack by many powerful acids and alkalis such as hydrofluoric acid and ammonia. It also acts as an effective corrosion barrier material.
Transparency
Graphene is also optically transparent in visible wavelengths, electri-cally and thermally conductive, and it adds only about 0.34 nm per lay-er to the total dimension of coated substrates. Graphene is chemically inert, stable in ambient atmosphere up to 400 °C, and can be grown on the meter-scale and mechanically transferred onto arbitrary surfaces. Single-layer graphene films and films consisting of a few layers of graphene also have good transparency. Therefore, thin graphene coatings, for example having up to 4 layers of graphene, do not significantly affect the optical properties of the underlying substrate. It has been demonstrated that graphene coatings retard microbially-induced galvanic corrosion (MIC) of metals for extended periods of time (2700 hours) as they prevent access of microbes to the surface, form a protective barrier and protect the surface from microbial by products that enhance Ni dissolution. A recent study however indicated that although graphene offers effective short-term oxidation protection, over long time scales it promotes more extensive wet corrosion than that seen for an initially bare, unprotected surface.
FISH SKIN COATING
Researchers at Leibniz Institute of Polymer Research have developed a structurally colored coating based on graphene flakes, that changes color depending on deformation of the colored surface.
Inspired by natural iridescence in fish skin, this coating could provide a simple way to warn of hidden damage in buildings, bridges and other structures. “The new material is a kind of traffic light to warn of hidden damage in buildings and vehicles, ” said Shanglin Gao at the Leibniz Institute of Polymer Research “as it changes colour depending on deformation. Normally, the coating is red; however, when deformed, it appears yellow, and when cracked at the micrometre scale, green. This colour-changing ability comes from a careful initial alignment of the graphene flakes in semi-transparent, parallel layers, coating a glass fibre. Under stress, the layers compress and flatten, changing the interference and colour of reflected light.”
Recent commercial news
Optics company LightPath Technologies Inc. has won a $200,000 award from the National Science Foundation (NSF) for its Small Business Innovation Research project. The project “Carbide bonded graphene coating for enhanced glass molding.” will seek to enhance the molding for both visible and infrared glasses when used for mold release.
Applied Graphene Materials has signed a joint development agreement with James Briggs to develop graphene-based anti-corrosive coatings. The company will incorporate graphene nanoplatelets into its existing paint formulations with a view to launching a new range of high performing primers in 2017.
Grox Industries, a University of Arkansas spin-out developing a graphene-based glass coating that improves the energy efficiency of windows, won first place at the University of Manitoba’s Stu Clark Investment Competition on March 11. Based on the research of U of A chemistry professor Ryan Tian, the company has developed a custom, graphene oxide-based window coating line called Helios. Compared to other coatings on the market, Helios absorbs more damaging ultraviolet light, while allowing more aesthetically pleasing visible light to pass through the window.
Grafoid has developed a patent pending GrafeneX graphene coatings technology. The company describes the GrafeneX technologies as a cost-effective way of laying down graphene coatings on large surface areas. GrafeneX is applied using a proprietary, room temperature, top-down process, designed as an inline continuous surface conversion process compatible with most conventional industrial coil-to-coil and roll-to-roll coating facilities.
